U.S. F-22 Raptors intercepted four Russian bombers and a pair of Su-35 Flanker-E fighter aircraft off the coast of Alaska on Monday, according to the North American Aerospace Defense Command, or NORAD. NORAD on Tuesday said that two F-22 stealth fighters initially intercepted two Tupolev Tu-95 Bear bombers. Following that intercept, two more F-22s intercepted a second group of two Russian bombers flanked by two of the Sukhoi-made fighters. While the aircraft remained in international airspace, they flew into North America's Air Defense Identification Zone, or the airspace surrounding the United States and Canada. The ADIZ stretches roughly 200 miles off Alaska's coast. "Our ability to deter and defeat threats to our citizens and vital infrastructure starts with detecting, tracking and positively identifying aircraft in our airspace," said Air Force Gen. Terrence O'Shaughnessy, commander of NORAD, in a statement posted on Twitter. "We are on alert 24 hours a day, seven days a week, 365 days a year." An E-3 airborne warning and control system, or AWACS, provided surveillance and support during the intercept, the command said. The incident comes as the Defense Department's biannual Northern Edge exercise is in full swing in Alaska. Approximately 10,000 U.S. military personnel are participating in the joint training exercise hosted by U.S. Pacific Air Forces (PACAF). The drills, being conducted at central Alaska ranges and the Gulf of Alaska, involve roughly 250 aircraft from the Air Force, Navy and Marine Corps, as well as five Navy ships, PACAF said earlier this month. The two-week-long exerciseconcludes May 24. Between 2016 and 2018, NORAD conducted 164 intercepts of foreign and civilian aircraft, according to statistics provided to Military.com. There are about half a dozen intercepts of foreign state aircraft per year, according to Canadian Lt. Gen. Christopher J. Coates, deputy commander of NORAD.